Development of humanised mouse model for DC based immunotherapy

Abstract

Dendritic cells (DCs) are professional antigen presenting cells (APC) that orchestrate the immune response. These cells play a major role in inducing primary immune response by activating naive CD8+ and CD4+ T cells. In mice, CD8+ DC is the major DC subset that excels in priming CD8+ T cells to become cytotoxic T cells (CTL), critical to induce anti-tumour and anti-viral immunity. Human peripheral blood, lymphoid and nonlymphoid organs contain 3 major DC subsets, plasmacytoid dendritic cells (pDCs), CD1c+ and CD141+ myeloid DCs, each with distinct functional characteristics. Comparative transcriptome analysis enabled close alignment of human and mouse DC subsets. However translating the knowledge obtained from the mouse to the human DC system has been hampered by differences such as the expression of pathogen recognition receptors (PRR), which necessitate the study on human DC for functional characterisation. Functional studies of human DC subsets have been limited due to their rarity, technical challenging isolation procedures and a lack of in vitro models. To overcome this limitation, mouse models of human haematopoetic stem cell (HSC) engraftment have been used and are referred to as humanised mice. Humanised mouse model represent a powerful tool to study various key aspects of human immune function. Here we describe the development and characterization of HLA-A2 transgenic NOD/SCID/IL2rg null (NSG-A2) mice for their ability to support human cord blood (CB)-derived HSC engraftment and multilineage differentiation. NSG-A2 mice were capable of developing human myeloid DC and pDC, B cells, T cells and monocytes in bone marrow (BM), spleen, liver, lung and peripheral blood by 10-14wks post injection. Transcriptional analysis demonstrated close alignment of BM-derived DC subsets from humanised NSG-A2 mice with human blood and tissue DC. The immunoactivation potential of different tolllike receptor (TLR) activators on human DC subsets in vivo was evaluated based on the expression of activation surface markers, differential gene expression using microarray and cytokine levels in serum by cytokine bead assay. All DC subsets purified from BM of humanised mice were capable of priming naive antigen (Ag)-specific CD8+ T cells to elicit a polyfunctional T cell response (CD107a, TNFa, IFNg, IL-2) against MART1 peptide. Thus, NSG-A2 mice engrafted with human CB-derived HSC is a useful in vivo long-lived model to investigate the functional and phenotypical characteristics of human DC subsets in both in vitro and in vivo settings. This will also be a powerful model for preclinical studies to design and validate novel immunotherapies and vaccines.